This invention relates to a four-cycle internal combustion engine lubrication system and more particularly to a lubrication system particularly adapted for use with four-cycle outboard motors.
For a variety of reasons, it has been proposed to substitute four-cycle engines for the more conventionally used two-cycle engines as power plants for outboard motors. One of the main reasons for this substitution is the fact that four-cycle engines may tend to be more environmentally suitable for this application than two-cycle engines.
One of the reasons for the preference of using four-cycle engines, however, also complicates the construction of the outboard motor. With a four-cycle engine, unlike a two-cycle engine, the lubricant is not spent and discharged from the combustion chamber of the engine. Rather, the lubricant is recirculated and hence not discharged to the atmosphere. This means, however, that there must be some provision within the outboard motor to hold adequate lubricant for engine lubrication for relatively long periods of time.
It generally has become the practice to position the oil reservoir for the engine in the upper portion of the drive shaft housing. This is done for a variety of reasons, not the least of which is to maintain a lower center of gravity for the power head. This, however, raises certain problems in connection with the design and configuration of the lubricating system for the engine.
Frequently, with normal four-cycle applications, the crankcase also forms the oil reservoir. This is done in so-called "wet sump" engines. However, in an outboard motor application, the engine is generally mounted in the power head so that its crankshaft extends about a vertically extending axis. This is done to facilitate connection of the engine output shaft to the drive shaft for the propulsion unit of the outboard motor. This means that the crankcase also extends vertically and conventional type of wet sump engines cannot be employed.
The positioning of the oil reservoir in the drive shaft housing presents some problems because of the use of this area for exhaust treatment. Nevertheless, this is generally the preferred location for the oil reservoir.
Thus, there becomes a problem in the design of the arrangement for retuning the lubricant to the oil reservoir from the engine. This problem is compounded when one or more overhead camshafts are employed. That is, in conventional vertical engine disposition, the cylinder head drains back into the crankcase chamber through the cylinder block. This is not as feasible, however, with vertical crankshaft positioning.
It is, therefore, a principal object of this invention to provide an improved oil drain arrangement for a four-cycle outboard motor having at least one overhead camshaft.
Also, it is generally the practice to utilize a crankcase ventilation system with engines for this purpose. However, in order to ventilate the crankcase and also return oil, care must be taken that the ventilating path does not overlap significantly with the oil return path. If it does, there is a danger that the ventilating gases may pick up large amounts of oil and deliver them into the ventilating system which is obviously undesirable.
It is, therefore, a still further object of this invention to provide an improved and simplified oil drain system for a four-cycle outboard motor wherein the drain passages are clear of the crankcase ventilating system.
The vertical positioning of the crankshaft also can give rise to certain problems in connection with drainage of the oil from the various components. This is particularly true in the crankcase area because of the provision of journals for the crankshaft. An arrangement must be provided that permits the oil to drain from the various bearings of the crankcase to the lower end and flow smoothly from the lower end back into the oil reservoir. It is, therefore, a still further object of this invention to provide an improved oil return system for the crankcase of a four-cycle outboard motor.